1. Field of the Invention
This invention relates to a method of and apparatus for the manufacture of plastic bags, e.g., for use as bin liners.
2. The Prior Art
It is well known to manufacture plastic bags from a continuous tube of extruded polyethylene. The extruded tubing is expanded to reduce the thickness of the polyethylene film, flattened, heat sealed and severed across the width of the tubing, such that the heat seals form the bottoms of the bags. Handles can be formed by removing an upper central section of the bags, and by providing a series of transverse perforation lines rather than severing the tubing, a series of bags which an be wound into a roll may be produced. In order to reduce the width of the rolls of bags, an to reduce the size of the machinery required for the bag manufacture, it is known to fold the sides of the tubing inwardly to form gussets prior to sealing. It is also known to fold the gusseted tubing prior to sealing as described in GB-A-1584746, which enables an especially strong seal to be produced. However, this folding method is not suitable for the manufacture of rolls of interconnected bags formed with hands, as the folding operation superimposes the handles at the same side of the folded tube, and the resulting string of bags cannot be satisfactorily wound into a roll. Handles at the open end of a bag are often desirable for tying closed the bag after it has been filled, e.g., with refuse, or to facilitate carrying the bag.
GB-A-2 274 446 addresses the drawbacks of the aforementioned folding method by providing a bag having laterally opposed gusseted side portions folded about longitudinal fold liens onto opposite sides of a medial portion.
The method of bag folding described in GB-A-2 274 446 secures the advantage of a strong base seal. It also enables manufacture of a bag with handles that, in its folded form, is considerably narrower than previously known bags with handles, and the handles of the folded bag may be located at laterally opposed sides of the bag which is desirable when a string of bags is to be wound into a wall.